Non-invasive, transdermal sampling of body fluids has long been a goal of medical research.
Prior an attempts to achieve this goal ate described in, tor instance U.S. Pat. No. 6,887,202 issued on May 3, 2005 to Currie et al. entitled “Systems and Methods for Monitoring health and Delivering Drugs Transdermally” the contents of which are hereby incorporated by reference.
The prior attempts at transdermal sampling have typically been characterized by making relatively large holes in the outermost layer of the epidermis, namely the stratum corneum which is effectively the surface of the skin and is composed mainly of dead cells that lack nuclei. The holes are typically made by heat or laser ablation or puncturing with fine needles and reach through to underlying, viable epidermis. Interstitial fluid from the viable epidermis or fluid from the extremity of the vascular system is then typically either sucked up, or squeezed out, from beneath the skin into the transdermal device where it is analyzed spectroscopically using systems of micro-fabricated channels and light guides.
Such systems have significant drawbacks, including the fact that the size of the holes is typically of the order of tens of microns which is sufficient to cause local irritation. this often results in inflammation, meaning that the channels typically cannot be maintained open for longer than a few hours to a few days.
Furthermore, micro-fabrication of complex systems typically requires the use of silicon substrates which are relatively inflexible, making close surface contact difficult and resulting in lateral motion between the transdermal detector and the holes through the stratum corneum. Because of the size of the transdermal holes, typically tens of microns in diameter, even a small amount of lateral motion renders such a device inoperative.
To achieve the goal of minimally invasive, continuous real-time trace transdermal sampling, analysis and delivery a system and method that overcomes these difficulties is needed.